CaCl2 molten salt hydrate-promoted conversion of carbohydrates to 5-hydroxymethylfurfural: an experimental and theoretical study
CaCl2 molten salt hydrate-promoted conversion of carbohydrates to 5-hydroxymethylfurfural: an experimental and theoretical study
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DOI：
10.1039/d0gc04356g
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发表时间：
2021-03-07
期刊：
影响因子：
9.8
通讯作者：
Ouyang, Pingkai
中科院分区：
文献类型：
--
作者：
Lin, Changqu;Chai, Chaoqun;Ouyang, Pingkai
碱土金属盐是环境友好和经济的。它们在生物质转化过程中，特别是在异构化和脱水过程中，引起了人们的广泛关注。然而，对碱土金属介导的催化机制缺乏了解阻碍了从葡萄糖或果糖实现高HMF产率。在此，我们进行了实验和理论研究氯化钙催化的葡萄糖到果糖异构化和果糖到HMF脱水。在CaCl 2溶液中，80 ℃时，葡萄糖的果糖产率最高（33.6%）。同时，在果糖至HMF脱水中存在CaCl 2显著提高了果糖转化率。设计了葡萄糖异构化-脱水一锅法合成HMF的工艺，转化率100%，HMF收率52.1%。CaCl 2溶液可以重复使用五次，同时保持催化活性而无需再生。通过H-1 NMR、C-13 NMR、DOSY-NMR和DFT计算，我们得出结论：β-吡喃葡萄糖互变异构体的C1/C2位与CaCl 2的配位促进了葡萄糖的1，2-分子内氢化物位移，从而使葡萄糖快速转化为果糖。类似地，Ca 2+可以与β-d-呋喃果糖的C2/C6-OH络合并稳定该互变异构体，其容易形成HMF。这是CaCl 2促进果糖制备HMF的主要原因。
Alkaline earth metal salts are environmentally friendly and economical. They have attracted much attention in the process of biomass conversion, especially for isomerization and dehydration. However, the lack of understanding of the alkaline earth metal-mediated catalytic mechanism prevents the achievement of high HMF yields from glucose or fructose. Herein, we performed experimental and theoretical studies on CaCl2-catalyzed glucose-to-fructose isomerization and fructose-to-HMF dehydration. In CaCl2 solution, the highest fructose yield (33.6%) from glucose can be achieved at 80 degrees C. Meanwhile, the presence of CaCl2 in fructose-to-HMF dehydration notably improved fructose conversion. A "one-pot" isomerization-dehydration of glucose to prepare HMF was designed and 100% conversion and 52.1% HMF yield were obtained. The CaCl2 solution can be reused for five runs while maintaining catalytic activity without regeneration. Through H-1 NMR, C-13 NMR, DOSY-NMR and DFT calculations, we concluded that the coordination between the C1/C2 sites of the beta-glucopyranose tautomer and CaCl2 promoted the 1,2-intramolecular hydride shift of glucose, thus rapidly converting glucose into fructose. Similarly, Ca2+ can complex with the C2/C6-OH of beta-d-fructofuranose and stabilize this tautomer, which easily forms HMF. This is the main reason that CaCl2 can promote the preparation of HMF from fructose.